Method and system for controlling the defrost cycle of a vapor compression system for increased energy efficiency

ABSTRACT

Operating a vapor compression system including determining a total heat delivered by the vapor compression system, determining a total electrical energy consumed by the vapor compression system while delivering heat, maintaining a total electrical energy consumed by the vapor compression system during a defrosting cycle, determining a cumulative coefficient of performance of the vapor compression system based on the total heat delivered, the total electrical energy consumed by the vapor compression system while delivering heat, and the total electrical energy consumed by the vapor compression system during the defrosting cycle, and initiating a defrosting cycle based the cumulative coefficient of performance.

TECHNICAL FIELD

The disclosure relates generally to vapor compression systems, and moreparticularly, to methods and systems for controlling the defrost cycleof vapor compression systems for increased energy efficiency.

BACKGROUND

Vapor compression systems are often used to provide heating and/orcooling to a controlled space. Example vapor compression systems includeheat pumps and air-conditioners that provide heating and/or cooling to abuilding for increased occupant comfort, and refrigeration units thatprovide cold storage for goods in the home, grocery stores, warehousesand other applications. Many vapor compression systems use a compressor,a condenser, an evaporator and an expansion valve to transfer heat fromone region to another. For example, during operation, a refrigerantpressurized by the compressor is cooled by a reduction in pressurethrough the expansion valve. The cooled refrigerant extracts heat viathe evaporator at a cold region. The heated refrigerant isre-pressurized by the compressor and delivered to the condenser. Thecondenser releases the heat to a hot region. This process is repeated totransfer heat from the cold region to the hot region.

When the cold region reaches a low ambient temperature, the surfacetemperature of the evaporator can fall below the dew point of air andbelow the freezing point of water, which can result in water vapor inthe air condensing on the outside of the evaporator and form a layer ofice. The layer of ice acts as thermal insulation on the evaporator andgradually reduces the efficiency of the evaporator and thus the vaporcompression system. Because of this known phenomenon, the ice istypically periodically eliminated by reversing the vapor compressionsystem for a short time, during what is referred to as a defrost cycle,which heats the evaporator and melts the ice. The defrost cycles notonly consumes significant electrical energy, but they also reverse theintended heating or cooling of the vapor compression system. Defrostingtoo early can waste energy by unnecessarily heating an evaporator thatis still operating relatively efficiently, and defrosting too late canwaste energy by operating the vapor compression system with a heavilyiced up evaporator.

In many vapor compression systems, defrosting cycles are controlled tooccur at regular fixed time intervals or at an interval that does nottake in account current operating condition. What would be desirable isa method and system to control the defrost cycles of a vapor compressionsystem in a manner that takes in account current operating conditions soas to increase the overall energy efficiency of the vapor compressionsystem.

SUMMARY

This disclosure relates generally to vapor compression system, and moreparticularly, to methods and systems for controlling the defrost cycleof vapor compression systems. In one example, a method of operating avapor compression system includes determining a measure related to atotal heat delivered (THD) by the vapor compression system following acompletion of a defrosting cycle, determining a measure related to atotal electrical energy consumed (TEC-H) by the vapor compression systemwhile delivering heat following completion of the defrosting cycle,maintaining a measure related to a total electrical energy consumed(TEC-D) by the vapor compression system during a previous defrostingcycle, determining a cumulative coefficient of performance (CCOP) of thevapor compression system based at least in part on the measure relatedto a total heat delivered (THD) by the vapor compression systemfollowing the completion of a defrosting cycle, the measure related to atotal electrical energy consumed (TEC-H) by the vapor compression systemwhile delivering heat following the completion of the defrosting cycle,and the measure related to a total electrical energy consumed (TEC-D) bythe vapor compression system during the defrosting cycle, and initiatinga next defrosting cycle at a time that is based at least in part on oneor more characteristics of the cumulative coefficient of performance(CCOP).

Alternatively or additionally to the foregoing, the vapor compressionsystem may include a compressor, a condenser, an evaporator and anexpansion valve. In some cases, the compressor and the evaporator maycirculate a refrigerant.

Alternatively or additionally to any of the embodiments above,determining the measure related to the total heat delivered (THD) by thevapor compression system following the completion of the defrostingcycle may include determining a speed of the compressor, sensing adischarge pressure of the refrigerant at an output of the compressor,and using the discharge pressure to identify a condensing temperature ofthe refrigerant, sensing a suction pressure of the refrigerant at aninput of the compressor, and using the suction pressure to identify anevaporating temperature of the refrigerant, and determining the measurerelated to the total heat delivered (THD) by the vapor compressionsystem based at least in part on the speed of the compressor, thecondensing temperature and the evaporating temperature.

Alternatively or additionally to any of the embodiments above, furtherincluding sensing a discharge temperature of the refrigerant at theoutput the compressor, and wherein the measure related to the total heatdelivered (THD) by the vapor compression system may be based at least inpart on the speed of the compressor, the condensing temperature, theevaporating temperature and the discharge temperature.

Alternatively or additionally to any of the embodiments above, furtherincluding sensing the discharge pressure and the suction pressure usingrespective pressure sensors.

Alternatively or additionally to any of the embodiments above, the CCOPmay be determined by dividing the measure related to a total heatdelivered (THD) by the sum of the measure related to the totalelectrical energy consumed (TEC-H) by the vapor compression system whiledelivering heat plus the measure related to the total electrical energyconsumed (TEC-D) by the vapor compression system during the defrostingcycle.

Alternatively or additionally to any of the embodiments above, themeasure related to the total electrical energy consumed (TEC-D) by thevapor compression system during the defrosting cycle may be an averageof the total electrical energy consumed (TEC-D) by the vapor compressionsystem during a previous “N” of the defrosting cycle, wherein “N” is aninteger greater than or equal to 1.

Alternatively or additionally to any of the embodiments above, the nextdefrosting cycle may be initiated at a time when the cumulativecoefficient of performance (CCOP) reaches a maximum (e.g. peak) value.

Alternatively or additionally to any of the embodiments above, the nextdefrosting cycle may be initiated at a time when a derivative of thecumulative coefficient of performance (CCOP) crosses zero.

Alternatively or additionally to any of the embodiments above, the vaporcompression system may include a heat pump system configured to heat abuilding.

Alternatively or additionally to any of the embodiments above, the vaporcompression system may include a refrigeration system.

In another example, a vapor compression system may include a compressorconfigured to pressurize a refrigerant, a condenser operatively coupledto the compressor and configured to receive the compressed refrigerantfrom the compressor, an evaporator operatively coupled to the compressorand configured to return expanded refrigerant to the compressor, anexpansion valve operatively coupled between the evaporator and thecondenser and configured to expand the compressed refrigerant, and acontroller operatively coupled to the compressor. The controller may beconfigured to record a heat delivered by the refrigerant and anoperational energy of the compressor during an operational period of thevapor compression system, determine a cumulative coefficient ofperformance (CCOP) of the system based on the recorded delivered heat,the recorded operational energy, and a defrost energy consumed by thecompressor during a previous defrost period of the vapor compressionsystem, and initiate a next defrost period of the vapor compressionsystem in response to the CCOP of the system meeting one or morepredefined conditions.

Alternatively or additionally to any of the embodiments above, furtherincluding a set of sensors operatively coupled to the controller, theset of sensors may be configured to sense a discharge pressure of therefrigerant at an output of the compressor and a suction pressure of therefrigerant at an input of the compressor, wherein the dischargepressure may be used to identify a condensing temperature of therefrigerant and the suction pressure is used to identify an evaporatingtemperature of the refrigerant.

Alternatively or additionally to any of the embodiments above, therecorded heat delivered by the refrigerant and the operational energy ofthe compressor may be based at least in part on the condensingtemperature of the refrigerant, the evaporating temperature of therefrigerant, and a speed of the compressor.

Alternatively or additionally to any of the embodiments above, the CCOPmay be determined by dividing the recorded delivered heat by the sum ofthe recorded operational energy plus the defrost energy consumed by thecompressor during the previous defrost period of the vapor compressionsystem.

Alternatively or additionally to any of the embodiments above, the nextdefrost period may be initiated at a time when the CCOP reaches amaximum value.

In another example, a non-transient computer readable medium mayincluding instructions stored thereon that when executed by a processorcause the processor to receive one or more sensed conditions of a vaporcompression system, using one or more of the sensed conditions todetermine a measure related to a total heat delivered (THD) by the vaporcompression system following a completion of a defrosting cycle, usingone or more of the sensed conditions to determine a measure related to atotal electrical energy consumed (TEC-H) by the vapor compression systemwhile delivering heat following the completion of the defrosting cycle,store a measure related to a total electrical energy consumed (TEC-D) bythe vapor compression system during a previous defrosting cycle,determining a cumulative coefficient of performance (CCOP) of the vaporcompression system based at least in part on the measure related to atotal heat delivered (THD) by the vapor compression system following thecompletion of a defrosting cycle, the measure related to a totalelectrical energy consumed (TEC-H) by the vapor compression system whiledelivering heat following the completion of the defrosting cycle, andthe measure related to a total electrical energy consumed (TEC-D) by thevapor compression system during the defrosting cycle, and initiating anext defrosting cycle of the vapor compression system at a time that isbased at least in part on one or more characteristics of the cumulativecoefficient of performance (CCOP).

Alternatively or additionally to any of the embodiments above, the nextdefrosting cycle may be initiated at a time when the cumulativecoefficient of performance (CCOP) reaches a maximum value.

Alternatively or additionally to any of the embodiments above, the vaporcompression system may include a compressor and an evaporatorcirculating a refrigerant. Additionally, determining the measure relatedto the total heat delivered (THD) by the vapor compression systemfollowing the completion of the defrosting cycle may include determininga speed of the compressor, sensing a discharge pressure of therefrigerant at an output of the compressor, and using the dischargepressure to identify a condensing temperature of the refrigerant,sensing a suction pressure of the refrigerant at an input of thecompressor, and using the suction pressure to identify an evaporatingtemperature of the refrigerant, and determining the measure related tothe total heat delivered (THD) by the vapor compression system based atleast in part on the speed of the compressor, the condensing temperatureand the evaporating temperature.

Alternatively or additionally to any of the embodiments above, furtherincluding sensing a discharge temperature of the refrigerant at theoutput the compressor, and wherein the measure related to the total heatdelivered (THD) by the vapor compression system may be based at least inpart on the speed of the compressor, the condensing temperature, theevaporating temperature and the discharge temperature.

The above summary of some illustrative embodiments is not intended todescribe each disclosed embodiment or every implementation of thepresent disclosure. The Figures and Description which follow moreparticularly exemplify these and other illustrative embodiments.

BRIEF DESCRIPTION OF THE FIGURES

The disclosure may be more completely understood in consideration of thefollowing description in connection with the accompanying drawings, inwhich:

FIG. 1 is a schematic view of an illustrative vapor compression system;

FIG. 2 is a schematic view of an illustrative computing device suitablefor controlling a vapor compression system;

FIG. 3A is a flow chart showing an illustrative method for determining ameasure related to the electrical energy consumed by the vaporcompression system;

FIG. 3B depicts an example of a compressor power consumption look-uptable;

FIG. 4A is a flow chart showing an illustrative method for determining ameasure related to a condenser heat rate of the vapor compressionsystem;

FIG. 4B depicts an example of a refrigerant mass flow look-up table;

FIG. 5 is a flow chart showing an illustrative method for initializing anext defrosting cycle or period of the vapor compression system; and

FIG. 6 is a graph depicting an example of a cumulative coefficient ofperformance (CCOP), a graph depicting an example of a derivative of theCCOP, and a resulting defrost request signal.

While the disclosure is amenable to various modifications andalternative forms, specifics thereof have been shown by way of examplein the drawings and will be described in detail. It should beunderstood, however, that the intention is not to limit the disclosureto the particular embodiments described. On the contrary, the intentionis to cover all modifications, equivalents, and alternatives fallingwithin the spirit and scope of the disclosure.

DESCRIPTION

For the following defined terms, these definitions shall be applied,unless a different definition is given in the claims or elsewhere inthis specification.

All numeric values are herein assumed to be modified by the term“about,” whether or not explicitly indicated. The term “about” generallyrefers to a range of numbers that one of skill in the art would considerequivalent to the recited value (i.e., having the same function orresult). In many instances, the terms “about” may include numbers thatare rounded to the nearest significant figure.

The recitation of numerical ranges by endpoints includes all numberswithin that range (e.g. 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, and5).

As used in this specification and the appended claims, the singularforms “a”, “an”, and “the” include plural referents unless the contentclearly dictates otherwise. As used in this specification and theappended claims, the term “or” is generally employed in its senseincluding “and/or” unless the content clearly dictates otherwise.

It is noted that references in the specification to “an embodiment”,“some embodiments”, “other embodiments”, etc., indicate that theembodiment described may include one or more particular features,structures, and/or characteristics. However, such recitations do notnecessarily mean that all embodiments include the particular features,structures, and/or characteristics. Additionally, when particularfeatures, structures, and/or characteristics are described in connectionwith one embodiment, it should be understood that such features,structures, and/or characteristics may also be used connection withother embodiments whether or not explicitly described unless clearlystated to the contrary.

The following description should be read with reference to the drawingsin which similar structures in different drawings are numbered the same.The drawings, which are not necessarily to scale, depict illustrativeembodiments and are not intended to limit the scope of the disclosure.Although examples of construction, dimensions, and materials may beillustrated for the various elements, those skilled in the art willrecognize that many of the examples provided have suitable alternativesthat may be utilized.

The current disclosure relates to devices, controllers, systems,computer programs, and methods adapted to initiate a defrosting cyclefor a vapor compression system. In some instances, the time at which thedefrosting cycle is initiated may be an optimal time with respect to theoverall cost of operating the vapor compression system, taking intoaccount both the electricity consumed by the vapor compression system todeliver temperature controlled air and the electricity consumed by thevapor compression system to perform a defrost cycle. For instance, insome cases, the total heat delivered (THD) by the vapor compressionsystem, the total electrical energy consumed (TEC-H) by the vaporcompression to deliver heat, and the total electrical energy consumed(TEC-D) by the vapor compression during a defrosting cycle may bedetermined. The THD, the TEC-H, and the TEC-D may then be used todetermine a cumulative coefficient of performance (CCOP) of the vaporcompression system that may indicate an optimal or desired time toinitiate a defrosting cycle for the vapor compression system.

FIG. 1 is a schematic view of an illustrative vapor compression system100 with a controller 102. The controller 102 may include an I/O port104 that communicates using a communication protocol. In some cases, thecommunication protocol may be an industry standard communicationprotocol such as BACNET, LONWORKS or Ethernet, for example, and in othercases it may be a proprietary communication protocol unique to themanufacturer of the controller 102 and/or components of vaporcompression system 100. The I/O port 104 of the controller 102facilitates access to, control of, and/or external communication to/fromthe vapor compression system 100. The controller 102 may be used tocontrol the vapor compression system 100. The controller 102 can beintegrated into the vapor compression system 100, or may be separatefrom the vapor compression system 100 and communicate with the vaporcompression system 100 via a wired or wireless interface. In some cases,the controller 102

In some cases, the illustrative vapor compression system 100 may includea liquid refrigerant that circulates through the vapor compressionsystem 100. In some instances, the vapor compression system 100 mayinclude an expansion valve 108, a condenser 110, a compressor 112, anevaporator 114, and a number of sensors 116 a-116 b. The controller 102may be configured to receive sensed signals from the sensors 116 a-116b, and control the operation of the compressor 112, the expansion valve108 and/or other components of the vapor compression system 100 asdesired. In some cases, the illustrative vapor compression system 100may provide heating and/or cooling to a building for increased occupantcomfort, such as a house, a retail store(s) (e.g., a supermarket,grocery store, mall, etc.), an office building, a factory/plant, aschool, etc. In other cases, the illustrative vapor compression system100 may be part of a refrigeration unit that provide cold storage forgoods in the home, grocery stores, warehouses and/or other applications.

It is noted that while one vapor compression system (e.g., vaporcompression system 100) is shown in FIG. 1, embodiments of the presentdisclosure are applicable to a plurality of vapor compression systems.In some cases, each vapor compression system may be controlled by acorresponding controller 102 designated specifically for that vaporcompression system. However, this is not required. In some instances, asingle local controller (e.g., the controller 102) may be used tocontrol several vapor compression systems. Moreover, some vaporcompression systems may include a single compressor that providescompressed refrigerant to multiple refrigerant circuits. In anotherexample, a vapor compression system may include a rack of compressorsthat supply compressed refrigerant to each of two or more independentlycontrolled circuits of the vapor compression system. In some cases, asingle local controller may control such a vapor compression system 100.In other cases, multiple controllers may control such a vaporcompression system.

In some examples, during an operational period, the refrigerant flows(e.g., circulates) through the illustrative vapor compression system 100of FIG. 1 in a counterclockwise direction. That is, the refrigerantpressurized by the compressor 112 is cooled by a reduction in pressurethrough the expansion valve 108. The cooled refrigerant extracts heatfrom air via the evaporator 114 at a cooler region, sometimes with theaid of fan 118. The heated refrigerant is re-pressurized by thecompressor 112 and delivered to the condenser 110. The condenser 110releases the heat at a hotter region. This process is repeated totransfer heat from the cooler region to the hotter region.

In some examples, the compressor 112 may be a fixed speed compressor. Inother examples, the compressor 112 may be a variable-speed or modulatingcompressor. In some instances, the controller 102 may determine thespeed, in real time, at which the compressor 112 operates to compressthe refrigerant. The controller 102 may record the TEC-H or theoperational energy consumed by the compressor 112 during the operationalperiod.

In some cases, sensors 116 a-116 b may be used to sense parameters,measurements, points, and/or other properties of the refrigerant, thevapor compression system 100, and/or components of the vapor compressionsystem 100. In some instances, the vapor compression system 100 mayinclude more or fewer sensors. In some examples, the sensors 116 a-116 bcan detect the measurements in real time. In some cases, the sensors 116a-116 b may include, but are not limited to, pressure sensors,temperature sensors, flow-rate sensors, position sensors, compositionsensors, chemical sensors, alarm sensors, etc.

In one particular example, the sensor 116 a may include a pressuresensor that can sense a discharge pressure of the refrigerant at theoutput of the compressor 112. In some instances, the controller 102 canreceive the sensed discharge pressure and identify a condensingtemperature of the refrigerant using the discharge pressure. The sensor116 a may include a temperature sensor that can sense a dischargetemperature of the refrigerant at the output of the compressor 112. Thecontroller 102 may adjust the speed of the compressor 112 as needed toincrease or decrease the pressure and/or temperature on the refrigerantat the output of the compressor 112.

After exiting the compressor 112, the hot compressed refrigerant flows(e.g., be routed) to the condenser 110. The condenser 110 condenses therefrigerant (e.g., superheated) vapor into a liquid. In some cases, thecondenser 110 can include a coil or tubes, and the condenser 110 cancondense the refrigerant vapor into a liquid by flowing the refrigerantthrough the coil or tubes while flowing cool water or cool air acrossthe coil or tubes, such that heat from the refrigerant is carried awayby the water or air. The condensed liquid refrigerant then flows to theexpansion valve 108. The expansion valve 108 can be configured to adjustthe pressure of the condensed liquid refrigerant downstream of theexpansion valve 108. The pressurized refrigerant is cooled by areduction in pressure through the expansion valve 108. In the exampleshown, the expansion valve 108 is controlled by controller 102 via adirect connection or a wired or wireless network(s) to decrease thepressure of the subcooled liquid refrigerant output from the condenser110. After flowing through the expansion valve 108, the refrigerantenters coil or tubes of the evaporator 114. A fan 118 may pass air fromcolder region across the coil or tubes carrying the refrigerant, whichcools the air (i.e. extracts heat from the air) and thus lowers thetemperature of the air. This may evaporate the refrigerant so that therefrigerant is once again a saturated vapor. The saturated vapor exitsevaporator 114 and flow to the compressor 112, and the cycle is repeatedto transfer heat from the colder region to the hotter region.

In some cases, the sensor 116 b may include a pressure sensor that cansense a suction pressure of the saturated refrigerant vapor after itexits the evaporator 114 and is input back into the compressor 112. Insome instances, the controller 102 can receive the sensed suctionpressure and identify an evaporating temperature of the refrigerantusing the suction pressure. In some examples, the controller 102 maydetermine and record a measure related to the THD by the vaporcompression system based on the speed of the compressor, the condensingtemperature of the refrigerant at the output of the compressor 112, theevaporating temperature of the refrigerant at the input of thecompressor 112, and the discharge temperature of the refrigerant at theoutput of the compressor 112. Moreover, in some examples, the controller102 may adjust the speed of the compressor 112 as needed to increase ordecrease the pressure and/or temperature of the refrigerant by acontrolled amount at the output of the compressor 112 based on thesensed suction pressure.

In many cases, vapor compression systems, such as the vapor compressionsystem 100, must deal with frosting. At low ambient temperatureconditions, the surface temperature of the evaporator 114 can fall belowthe dew point of humid air and below the freezing point of water,resulting in the water vapor contained in the air being deposited on theevaporator 114 in the form of ice. In this instance, the controller 102may place the vapor compression system 100 in a defrost cycle or period.In one example, during the defrost cycle, the refrigerant can again flowthrough the vapor compression system 100 in a counterclockwisedirection. During this time, the TEC-D or defrost energy is used by thecompressor 112 to compress the vapor refrigerant into a higher pressurevapor. However, in this instance, the hotter, compressed refrigerantvapor can flow directly to the evaporator 114 to help melt the ice thathas built up on the evaporator 114. To shorten the duration of thedefrost cycle, in some cases, the fan 118 may be turned off to decreasethe air flow across the evaporator 114 and thus decrease the amount ofheat extracted heat from the hot compressed refrigerant vapor that wouldhave otherwise been used to defrost the evaporator 114. Once the ice hasbeen sufficiently removed from the evaporator 114, the controller 102may place the vapor compression system 100 back in an operationalperiod.

In some cases, the controller 102 may use the THD, the TEC-H, and theTEC-D to determine an efficiency of performance of the vapor compressionsystem 100. In some instances, the controller 102 may initiate a defrostcycle for the vapor compression system in response to the determinedefficiency of performance meeting one or more predefined conditions orthresholds. For example, an optimal time for the vapor compressionsystem 100 to enter a defrost cycle, given the current operatingconditions, may be when the vapor compression system 100 has reached amaximum cumulative operating efficiency. In some examples, thecumulative operating efficiency of the vapor compression system 100 maybe represented as a Cumulative Coefficient Of Performance (CCOP) givenby:CCOP=THD/(TEC-H+TEC-D)  Equation (1)

In this example, when the CCOP reaches a maximum, that is, when thederivative of the CCOP crosses zero, the controller 102 may determinethat the vapor compression system 100 has reached the optimal time toinitiate a defrost cycle for the evaporator 114.

FIG. 2 depicts a schematic of an illustrative controller device 200. Thecontroller device 200 is only one example of a suitable computing deviceand is not intended to suggest any limitation as to the scope of use orfunctionality of embodiments described herein. Regardless, it iscontemplated that the controller device 200 is capable of beingimplemented and/or performing any of the functionality set forth herein.

The illustrative controller device 200 may be configured to control avapor compression system (e.g., vapor compression system 100 of FIG. 1).In some cases, the controller device 200 may be implemented using ageneral purpose and/or special purpose computing environment. In somecases, the controller 200 may be local to the vapor compression system100, while in other cases the controller 200 may be remote from thevapor compression system 100. In some cases, part of the controller 200is local to the vapor compression system 100, and part of the controller200 may be remote (e.g. in the cloud). These are just examples.

The controller device 200 may be described in the general context ofcomputer system executable instructions, such as program modules, beingexecuted by a computing device. Generally, program modules may includeroutines, programs, objects, components, logic, data structures, and soon that perform particular tasks or implement particular datamanipulation functions. In some cases, the controller device 200 may bepracticed in distributed cloud computing environments where tasks areperformed by remote processing devices that are linked through acommunications network. In a distributed cloud computing environment,program modules may be located in both local and remote computer systemstorage media including memory storage devices.

As shown in FIG. 2, the illustrative controller device 200 may include,but are not limited to, one or more processors 202, a system memory 204,and a bus 206 that couples various system components including systemmemory 204 to the processor 202.

The bus 206 may represent one or more of any of several types of busstructures, including a memory bus or memory controller, a peripheralbus, an accelerated graphics port, and a processor or local bus usingany of a variety of bus architectures. By way of example, and notlimitation, such architectures may include Industry StandardArchitecture (ISA) bus, Micro Channel Architecture (MCA) bus, EnhancedISA (EISA) bus, Video Electronics Standards Association (VESA) localbus, and Peripheral Component Interconnect (PCI) bus. In some cases, thebus may be implemented using a proprietary bus architecture.

In some instances, the processor 202 may include a pre-programmed chip,such as a very-large-scale integration (VLSI) chip and/or an applicationspecific integrated circuit (ASIC). In such embodiments, the chip may bepre-programmed with control logic in order to control the operation ofthe controller device 200. In some cases, the pre-programmed chip mayimplement a state machine that performs the desired functions. By usinga pre-programmed chip, the processor 202 may use less power than otherprogrammable circuits (e.g. general purpose programmablemicroprocessors) while still being able to maintain basic functionality.In other instances, the processor 202 may be a programmablemicroprocessor. Such a programmable microprocessor may allow a user tomodify the control logic of the controller device 200 even after it isinstalled in the field (e.g. firmware/software updates), which may allowfor greater flexibility of the controller device 200 in the field overusing a pre-programmed ASIC.

The controller device 200 may include a variety of computer systemreadable media. Such media may be any available media that is accessibleby the controller device 200, and may include volatile and/ornon-volatile media, removable and non-removable media.

The illustrative controller device 200 may include computer systemreadable media in the form of volatile memory, such as random accessmemory (RAM) 208 and/or cache memory 210. The controller device 200 mayfurther include other removable/non-removable, volatile/non-volatilecomputer system storage media. By way of example only, storage system212 can be provided for reading from and writing to a non-removable,non-volatile magnetic media (not shown and typically called a “harddrive”). Although not shown, a magnetic disk drive for reading from andwriting to a removable, non-volatile magnetic disk (e.g., a “floppydisk”), and an optical disk drive for reading from or writing to aremovable, non-volatile optical disk such as a CD-ROM, DVD-ROM, EPROM,flash memory (e.g., NAND flash memory), an external SPI flash memory orother optical media can be provided. In such instances, each can beconnected to the bus 206 by one or more data media interfaces. As willbe further depicted and described below, memory 204 may include at leastone program product having a set (e.g., at least one) of program modules(e.g., software) that are configured to carry out the functions ofembodiments of the disclosure.

Program/utility 214, having a set (e.g., at least one) of programmodules 216, may be stored in memory 204 by way of example, and notlimitation, as well as an operating system, one or more applicationprograms (e.g., a vapor compression system control application 218, lookup tables 228, etc.), and/or other program modules and program data.Each of the operating system, one or more application programs, otherprogram modules and program data or some combination thereof, mayinclude an implementation of a networking environment. Program modules216 generally carry out the functions and/or methodologies ofembodiments of the disclosure as described herein. In some cases, theprogram modules 216 and/or the application programs (e.g., vaporcompression system control application 218 and the look up tables 228)may include assembler instructions, instruction-set-architecture (ISA)instructions, machine instructions, machine dependent instructions,microcode, firmware instructions, state-setting data, or either sourcecode or object code written in any combination of one or moreprogramming languages, including an object oriented programming languagesuch as Smalltalk, C++ or the like, and conventional proceduralprogramming languages, such as the “C” programming language or similarprogramming languages.

The controller device 200 may also communicate with one or more externaldevices 220 such as a keyboard, a pointing device, a display, etc.; oneor more devices that facilitate a user in interacting with thecontroller device 200; and/or any devices (e.g., network card, modem,wireless network card, etc.) that facilitate the controller device 200in communicating with one or more other remote device(s) 222 such as,for example, the vapor compression system 100, a field device, a smartphone, tablet computer, laptop computer, personal computer, PDA, and/orthe like. Such communication with the external device 220 can occur viaInput/Output (I/O) interfaces 224. Still yet, the controller device 200can communicate with the external devices 220 and/or the remote devices222 over one or more networks such as a local area network (LAN), ageneral wide area network (WAN), and/or a public network (e.g., theInternet) via network adapter 226. As depicted, the I/O interfaces 224and the network adapter 226 communicate with the other components of thecontroller device 200 via bus 206. In some cases, the remote devices 222may provide a primary and/or a secondary user interface for the user tointeract with the controller device 200. In some cases, the controllerdevice 200 may utilize a wireless protocol to communicate with theremote devices 222 over a wireless network.

As stated above, in some cases, the remote device(s) 222 may include thevapor compression system 100 (shown in FIG. 1). In some examples, theprocessor 202 may control the vapor compression system 100 by receivingsensor and/or other data from the vapor compression system 100 and/orother external information (e.g. weather information, etc.), and

sending input commands to vapor compression system 100. In some cases, acommand may be an instruction, order, or directive and may include ahigh-level goal (e.g., initiating a defrosting cycle for the vaporcompression system 100) that is sent to a local controller of the avapor compression system 100, or one or more low-level instructions(e.g., increasing/decreasing the speed of the compressor 112,increasing/decreasing the speed of the fan 118, turning on/off the fan118, etc.) that is sent to directly control the vapor compression system100.

It is contemplated that the vapor compression system control application218 may provide instructions to the processor 202 for initializing adefrost cycle for the vapor compression system 100. In some instances,the vapor compression system control application 218 and the look uptables 228 may execute entirely on the controller device 200, as astand-alone software package, and/or partly on the controller device 200and partly on the remote devices 222, such as for example, a locationcontroller of the vapor compression system 100.

FIG. 3A is a flow chart showing an illustrative method 350 fordetermining a measure related to the electrical energy consumed by thevapor compression system 100 that may be implemented as part of thevapor compression system control application 218. As shown in FIG. 3A,in some cases, during an operational period of the vapor compressionsystem 100, the vapor compression system control application 218 mayprovide instructions to the processor 202 to obtain signals from thesensors 116 a-116 b and the compressor 112 that indicate a dischargepressure 300 of a refrigerant from the compressor 112, a suctionpressure 302 of the refrigerant to the compressor 112, and a speed ofthe compressor 112. In some instances, the processor 202 may use thedischarge pressure 300 to determine/identify a condensing temperature306 of the refrigerant and the suction pressure 302 todetermine/identify an evaporating temperature 308 of the refrigerant. Insome cases, the vapor compression system control application 218 mayprovide instructions to the processor 202 to access the look up tables228 and reference a compressor power consumption look up table 310 thatis specific to the particular compressor used in the vapor compressionsystem 100. Moreover, the vapor compression system control application218 may provide instructions to the processor 202 to use the condensingtemperature 306, the evaporating temperature 308, and the compressorspeed 304 as indexes to the compressor power consumption look up table310 to identify an electrical energy consumed 312 by the vaporcompression system 100/compressor 112.

FIG. 3B depicts an example of compressor power consumption look up table310. As shown, the electrical energy consumed by the vapor compressionsystem 100/compressor 112 may be dependent on the condensing temperature306, the evaporating temperature 308, and the compressor speed 304. Forexample, when the compressor speed 304 is 30 rps, the condensingtemperature 306 is 40° C., and the evaporating temperature 308 is −25°C., the electrical energy consumed 312 by the compressor 112 is 843 W.In another example, when the compressor speed 304 is 60 rps, thecondensing temperature 306 is 50° C., and the evaporating temperature308 is −10° C., the electrical energy consumed by the compressor 112 is2526 W. In yet a further example, when the compressor speed 304 is 90rps, the condensing temperature 306 is 60° C., and the evaporatingtemperature 308 is 10° C., the electrical energy consumed by thecompressor is 5726 W.

Turning to FIG. 4A, the method 350 may also determining a measurerelated to a condenser heat rate of the vapor compression system 100. Asshown in FIG. 4A, during the operational period of the vapor compressionsystem 100, the processor 202 may obtain the discharge pressure 300 ofthe refrigerant, the suction pressure 302 of the refrigerant, and thespeed of the compressor 112. The vapor compression system controlapplication 218 may provide instructions to the processor 202 to obtainsignals from the sensors 116 a-116 b and the compressor 112 thatindicate a discharge temperature 400 of the refrigerant. The processor202 may use the discharge pressure 300 to determine/identify thecondensing temperature 306 of the refrigerant and an electricalexpansion valve 108 (EEV) inlet enthalpy 402. The processor 202 may usethe suction pressure 302 to determine/identify the evaporatingtemperature 308 of the refrigerant. The processor 202 may use thedischarge temperature 400 and the discharge pressure 300 todetermine/identify a discharge enthalpy 404 of the vapor compressionsystem 100. In some cases, the vapor compression system controlapplication 218 may provide instructions to the processor 202 to accessthe look up tables 228 and reference a refrigerant mass flow look uptable 406. The vapor compression system control application 218 mayprovide instructions to the processor 202 to use the condensingtemperature 306, the evaporating temperature 308, and the compressorspeed 304 to identify, from the refrigerant mass flow look up table 406,a mass flow rate (e.g. kg/s) of the refrigerant.

FIG. 4B depicts an example of the refrigerant mass flow look up table406. As shown, the mass flow rate of the refrigerant may be dependent onthe condensing temperature 306, the evaporating temperature 308, and thecompressor speed 304. For example, when the compressor speed 304 is 30rps, the condensing temperature 306 is 40° C., and the evaporatingtemperature 308 is −25° C., the mass flow rate of the refrigerant is32.90 kg/h. In another example, when the compressor speed 304 is 60 rps,the condensing temperature 306 is 50° C., and the evaporatingtemperature 308 is −10° C., the mass flow rate of the refrigerant is126.50 kg/h. In yet a further example, when the compressor speed 304 is90 rps, the condensing temperature 306 is 60° C., and the evaporatingtemperature 308 is 10° C., the mass flow rate of the refrigerant is390.50 kg/h.

Turning back to FIG. 4A, in some cases, a difference block 408calculates a difference of the discharge enthalpy 404 and the EEV inletenthalpy 402. At multiplication block 410, the processor 202 may takethe product of the mass flow rate of the refrigerant and the differenceof the discharge enthalpy 404 and the EEV inlet enthalpy 402 todetermine a condenser heat rate (e.g. kW) 412.

FIG. 5 is a flow chart showing an illustrative method 500 forinitializing a next defrosting cycle or period for the vapor compressionsystem 100. As shown in FIG. 5, the controller device 200/processor 202may maintain/store a TEC-D 502 by the vapor compression system 100during a previous defrosting cycle. In some examples, the TEC-D 502 maybe an average of the TEC-D during a previous “N” defrosting cycles,wherein “N” is an integer greater than 1. In some examples, the TEC-D502 may be obtained using a method similar to that shown in FIG. 3A, butduring the previous defrost cycle rather than during an operationalcycle. In this context, the defrost cycle is interposed between twooperational cycles. In some cases, the TEC-D 502 may be provided as afixed value by an installer/technician. At step 504, vapor compressionsystem control application 218 may provide instructions to the processor202 to integrate the electrical energy consumed 312 (see FIG. 3A) whilethe vapor compression system 100 is delivering heat during a currentoperational cycle following completion of a defrosting cycle, in orderto determine and record a measure related to a total energy consumed bythe compressor TEC-H 506 during the current operational cycle of thevapor compression system 100. Similarly, at step 508, vapor compressionsystem control application 218 may provide instructions to the processor202 to integrate the condenser heat rate 412 (see FIG. 4A) while thevapor compression system 100 is delivering heat during a currentoperational cycle following completion of a defrosting cycle, in orderto determine and record a measure related to a total condenser heatprovided by the compressor THD 510 during the current operational cycleof the vapor compression system 100. At step 512, the vapor compressionsystem control application 218 may provide instructions to the processor202 to obtain a sum of the TEC-H 506 and the TEC-D 502. At step 514, thevapor compression system control application 218 may provideinstructions to the processor 202 to divide the THD 510 by the sum ofthe TEC-H 506 and the TEC-D 502 (i.e., CCOP=THD/(TEC-H+TEC-D)) todetermine a current CCOP 516 of the vapor compression system 100.

Turning briefly to FIG. 6, a top graph 600 depicts an example of theCCOP 516 during an operational cycle where the vapor compression system100 is delivering heat. As shown in graph 600, the CCOP 516 starts atzero since the THD 510 is equal to zero when the operational cyclesbegins (following a defrost cycle). As time progresses, the THD 510begins to increase, causing an increase in the CCOP 516, as shown by therise in graph 600. However, the TEC-H 506 also increases as timeprogresses. As ice builds up on the evaporator 114, the evaporatorbecomes less efficient, and the TEC-H 506 increases at a faster ratethan the THD 510, thus causing the slope of the CCOP 516 to decreaseover time, eventually rolling over to a negative slope as shown in graph600. The CCOP 516 reaches a maximum at point 602 when the slope (i.e.derivative) of the CCOP 516 curve equals zero.

Turning back to FIG. 5, block 532 may operate as a differentiator tocalculate the derivative (i.e. slope) of the CCOP 516. At step 518, thevapor compression system control application 218 may provideinstructions to the processor 202 to obtain a product of the condenserheat rate 412 and the sum of the TEC-H 506 and the TEC-D 502 (i.e.,condenser heart rate×(TEC-H+TEC-D)). Similarly, the vapor compressionsystem control application 218 may provide instructions to the processor202 to obtain a product of the THD 510 and the electrical energyconsumed 312 (i.e., THD×electrical energy consumed). At step 522, thevapor compression system control application 218 may provideinstructions to the processor 202 to obtain a difference of (condenserheart rate×(TEC-H+TEC-D)) and (THD×electrical energy consumed) (i.e.,condenser heart rate×(TEC-H+TEC-D)−(THD×electrical energy consumed)). Atstep 524, the vapor compression system control application 218 mayprovide instructions to the processor 202 to obtain a quotient of(condenser heart rate×(TEC-H+TEC-D)−(THD×electrical energy consumed))and a square of the sum of the TEC-H 506 and the TEC-D 502 (i.e.,(condenser heart rate×(TEC-H+TEC-D)−(THD×electrical energyconsumed))/(TEC-H+TEC-D)−2) to obtain a derivative of the CCOP 526.Additionally, at step 528, the vapor compression system controlapplication 218 may provide instructions to the processor 202 to comparethe derivative (i.e. slope) of the CCOP 526 to zero. In some cases, ifthe derivative of the CCOP 526 is greater than zero, the vaporcompression system 100 may continue to deliver heat during theoperational period. However, if the derivative of the CCOP 526 is lessthan or equal to zero, it may be determined that the vapor compressionsystem 100 is running at or has passed its most efficient state due toice build-up (i.e., the CCOP 516 has reached or has passed its maximumvalue). Accordingly, at step 530, the vapor compression system controlapplication 218 may provide instructions to the processor 202 toinitiate the next defrosting cycle for the vapor compression system 100.upon receiving the initiation instructions, the vapor compression system100 may begin the next defrost cycle to melt the accumulated icebuild-up on the evaporator 114.

Turning again to FIG. 6, a bottom graph 604 depicts an example of thederivative of the CCOP 526 during an operational cycle where the vaporcompression system 100 is delivering heat. As shown in graph 604, thederivative of the CCOP 526 is at a maximum when the incremental increase(i.e., slope) of the CCOP 516 is greatest. As discussed in regard tograph 600, as time progresses, the TEC-H 506 increases. The increasingTEC-H 506 causes the derivative of the CCOP 516 to decrease. As icebuilds up on the evaporator 114, the evaporator becomes less efficient,and the TEC-H 506 increases at a faster rate than the THD 510, thuscausing the slope of the CCOP 516 to decrease over time, eventuallyrolling over to a negative slope at point 602 as shown in graph 600. TheCCOP 516 reaches a maximum at point 602 when the slope (i.e. derivative)of the CCOP 516 curve equals zero. The defrost request signal is shownat 606, which switches state from low to high when the derivative of theCCOP 516 crosses zero.

Although the present system and/or approach has been described withrespect to at least one illustrative example, many variations andmodifications will become apparent to those skilled in the art uponreading the specification. It is therefore the intention that theappended claims be interpreted as broadly as possible in view of therelated art to include all such variations and modifications.

What is claimed is:
 1. A method of operating a vapor compression systemthat has a compressor and an evaporator, wherein the vapor compressionsystem is configured to produce heat during a heating cycle and defrostthe evaporator of the vapor compression system during a defrostingcycle, the method comprising: determining a measure related to a totalheat delivered (THD) by the vapor compression system following acompletion of a defrosting cycle; determining a measure related to atotal electrical energy consumed (TEC-H) by the vapor compression systemwhile delivering heat following completion of the defrosting cycle;maintaining a measure related to a total electrical energy consumed(TEC-D) by the vapor compression system during a previous defrostingcycle; determining a cumulative coefficient of performance (CCOP) of thevapor compression system based at least in part on the measure relatedto a total heat delivered (THD) by the vapor compression systemfollowing the completion of a defrosting cycle, the measure related to atotal electrical energy consumed (TEC-H) by the vapor compression systemwhile delivering heat following the completion of the defrosting cycle,and the measure related to a total electrical energy consumed (TEC-D) bythe vapor compression system during the defrosting cycle; and initiatinga next defrosting cycle at a time that is based at least in part on oneor more characteristics of the cumulative coefficient of performance(CCOP).
 2. The method of claim 1, wherein the compressor and theevaporator circulate a refrigerant.
 3. The method of claim 1, whereindetermining the measure related to the total heat delivered (THD) by thevapor compression system following the completion of the defrostingcycle comprises: determining a speed of the compressor; sensing adischarge pressure of the refrigerant at an output of the compressor,and using the discharge pressure to identify a condensing temperature ofthe refrigerant; sensing a suction pressure of the refrigerant at aninput of the compressor, and using the suction pressure to identify anevaporating temperature of the refrigerant; and determining the measurerelated to the total heat delivered (THD) by the vapor compressionsystem based at least in part on the speed of the compressor, thecondensing temperature and the evaporating temperature.
 4. The method ofclaim 3, further comprising sensing a discharge temperature of therefrigerant at the output the compressor, and wherein the measurerelated to the total heat delivered (THD) by the vapor compressionsystem is based at least in part on the speed of the compressor, thecondensing temperature, the evaporating temperature and the dischargetemperature.
 5. The method of claim 4, further comprising sensing thedischarge pressure and the suction pressure using respective pressuresensors.
 6. The method of claim 1, wherein the CCOP is determined bydividing the measure related to a total heat delivered (THD) by the sumof the measure related to the total electrical energy consumed (TEC-H)by the vapor compression system while delivering heat plus the measurerelated to the total electrical energy consumed (TEC-D) by the vaporcompression system during the defrosting cycle.
 7. The method of claim6, wherein the measure related to the total electrical energy consumed(TEC-D) by the vapor compression system during the defrosting cycle isan average of the total electrical energy consumed (TEC-D) by the vaporcompression system during a previous “N” of the defrosting cycle,wherein “N” is an integer greater than or equal to
 1. 8. The method ofclaim 6, wherein the next defrosting cycle is initiated at a time whenthe cumulative coefficient of performance (CCOP) reaches a maximumvalue.
 9. The method of claim 6, wherein the next defrosting cycle isinitiated at a time when a derivative of the cumulative coefficient ofperformance (CCOP) crosses zero.
 10. The method of claim 1, wherein thevapor compression system comprises a heat pump system configured to heata building.
 11. The method of claim 1, wherein the vapor compressionsystem comprises a refrigeration system.
 12. A vapor compression systemcomprising: a compressor configured to pressurize a refrigerant; acondenser operatively coupled to the compressor and configured toreceive the compressed refrigerant from the compressor; an evaporatoroperatively coupled to the compressor and configured to return expandedrefrigerant to the compressor; an expansion valve operatively coupledbetween the evaporator and the condenser and configured to expand thecompressed refrigerant; a controller operatively coupled to thecompressor and configured to: record a heat delivered by the refrigerantand an operational energy of the compressor during an operational periodof the vapor compression system; determine a cumulative coefficient ofperformance (CCOP) of the system based on the recorded delivered heat,the recorded operational energy, and a defrost energy consumed by thecompressor during a previous defrost period of the vapor compressionsystem; and initiate a next defrost period of the vapor compressionsystem in response to the CCOP of the system meeting one or morepredefined conditions.
 13. The vapor compression system of claim 12,further comprising: a set of sensors operatively coupled to thecontroller, the set of sensors configured to sense a discharge pressureof the refrigerant at an output of the compressor and a suction pressureof the refrigerant at an input of the compressor, wherein the dischargepressure is used to identify a condensing temperature of the refrigerantand the suction pressure is used to identify an evaporating temperatureof the refrigerant.
 14. The vapor compression system of claim 13,wherein the recorded heat delivered by the refrigerant and theoperational energy of the compressor is based at least in part on thecondensing temperature of the refrigerant, the evaporating temperatureof the refrigerant, and a speed of the compressor.
 15. The vaporcompression system of claim 13, wherein the CCOP is determined bydividing the recorded delivered heat by the sum of the recordedoperational energy plus the defrost energy consumed by the compressorduring the previous defrost period of the vapor compression system. 16.The vapor compression system of claim 15, wherein the next defrostperiod is initiated at a time when the CCOP reaches a maximum value. 17.A non-transient computer readable medium comprising instructions storedthereon that when executed by a processor cause the processor to:receive one or more sensed conditions of a vapor compression system;using one or more of the sensed conditions to determine a measurerelated to a total heat delivered (THD) by the vapor compression systemfollowing a completion of a defrosting cycle; using one or more of thesensed conditions to determine a measure related to a total electricalenergy consumed (TEC-H) by the vapor compression system while deliveringheat following the completion of the defrosting cycle; store a measurerelated to a total electrical energy consumed (TEC-D) by the vaporcompression system during a previous defrosting cycle; determining acumulative coefficient of performance (CCOP) of the vapor compressionsystem based at least in part on the measure related to a total heatdelivered (THD) by the vapor compression system following the completionof a defrosting cycle, the measure related to a total electrical energyconsumed (TEC-H) by the vapor compression system while delivering heatfollowing the completion of the defrosting cycle, and the measurerelated to a total electrical energy consumed (TEC-D) by the vaporcompression system during the defrosting cycle; and initiating a nextdefrosting cycle of the vapor compression system at a time that is basedat least in part on one or more characteristics of the cumulativecoefficient of performance (CCOP).
 18. The non-transient computerreadable medium of claim 17, wherein the next defrosting cycle isinitiated at a time when the cumulative coefficient of performance(CCOP) reaches a maximum value.
 19. The non-transient computer readablemedium of claim 17, wherein the vapor compression system includes acompressor and an evaporator circulating a refrigerant, and whereindetermining the measure related to the total heat delivered (THD) by thevapor compression system following the completion of the defrostingcycle comprises: determining a speed of the compressor; sensing adischarge pressure of the refrigerant at an output of the compressor,and using the discharge pressure to identify a condensing temperature ofthe refrigerant; sensing a suction pressure of the refrigerant at aninput of the compressor, and using the suction pressure to identify anevaporating temperature of the refrigerant; and determining the measurerelated to the total heat delivered (THD) by the vapor compressionsystem based at least in part on the speed of the compressor, thecondensing temperature and the evaporating temperature.
 20. Thenon-transient computer readable medium of claim 19, further comprisingsensing a discharge temperature of the refrigerant at the output thecompressor, and wherein the measure related to the total heat delivered(THD) by the vapor compression system is based at least in part on thespeed of the compressor, the condensing temperature, the evaporatingtemperature and the discharge temperature.